e
Nod3-
C
Digital Transmitter
e
Nod3-
C
:
User’s instructions
NU-eNod3C-E-0911_165702-I
16/22
9 FILTERS:
There are four available filtering levels:
∗
filtering related to the A/D conversion rate including rejection of the mains frequency
(50 or 60 Hz) harmonics.
∗
2
nd
, 3
rd
or 4
th
order low-pass Bessel/Butterworth filter
∗
2
nd
order band-stop filter
∗
self-adaptive
filter
-
Filtering related to the A/D conversion rate :
the signal resolution is related to the conversion
rate. The conversion rate might be choosen as low as possible, particularly for static applications.
For dynamic applications, a compromise must be found between the measurement rate and the
low-pass filter cut-off frequency. The
e
Nod
View
software can be used to determine appropriate
filter values.
Choose a measurement rate that rejects the mains frequency harmonics according to the place of
use, 50 or 60Hz.
-
Bessel or Butterworth type low pass filter :
a low-pass digital filter can be applied as an output
of the A/D converter. The filter order is configurable (available values are 2, 3 or 4) and the
coefficients that define it depend on the A/D conversion rate, the wanted cutt-off frequency and on
the choosen order. These coefficients can be easily calculated by
e
Nod
View
software.
-
Band-stop filter :
a 2
nd
order band-stop filter might be applied as an output of the low-pass filter
(if used) or the A/D converter. It allows to attenuate the frequencies within a band defined by a high
and a low cut-off frequencies. The coefficients that define it depend on the A/D conversion rate and
the wanted cutt-off frequencies (that means the frequency band width). These coefficients can be
easily calculated by
e
Nod
View
software.
-
Self-adaptive filter
: this filter can be set in cascade after previous filters. It is particularly efficient
for static measurements but avoid using it in dynamic or dosing processes. The aim of this filter is
to eliminate erratic measurements and to average consistent measurements.
